1. Field of the Invention
The present invention relates to a hose having a resin layer as an inner layer and is suited for transporting hydrocarbon, such as gasoline, light oil, compressed natural gas, liquefied petroleum gas, and for transporting hydrogen, dimethyl ether, alcohol, warm water, and air-conditioning refrigerant. More particularly, the invention relates to a hose having a sealing layer, which is made of an elastic material, on the inner surface of a connecting portion at an end part thereof, to a direct-connect assembly formed by connecting this hose to a metal pipe, and to a method of manufacturing this hose.
2. Description of the Related Art
Hitherto, hoses each having a resin layer as an innermost layer have been used for piping of vehicles.
For example, a hose having a fluororesin layer as an innermost layer has been used as a hose for transporting an automotive fuel.
The gasoline permeability resistance of the hose for transporting fuel can be enhanced by providing the fluororesin layer as an innermost layer therein.
In a case where such a hose is connected to a counterpart metal pipe, a resin joint, which is what is called a quick connector, has hitherto been used.
For example, JP-A-8-270875 discloses a hose connecting structure using this joint.
FIG. 11 specifically shows this hose connecting structure. Herein, a resin joint 202 is preliminarily attached to an end part of a hose 200. Then, a counterpart metal pipe 204 is inserted thereto thereby to connect the hose 200 to the metal pipe 204 through the joint 202 so that the metal pipe 204 is prevented from slipping off the hose 200. O-rings 206 mounted in the joint 202 seal therebetween.
However, in a case where the hose 200 and the metal pipe 204 are connected to each other by using such a resin joint 202, there is a fear that the joint 202 hits against other components and gets crashed at automobile collision accidents. Thus, it has been studied that the metal pipe and the hose are directly connected to each other without using the joint 202.
This technique has an advantage in that the number of steps of an assembling process performed on an automotive assembly line can be reduced by one by preliminarily connecting the metal pipe directly to the hose to form a direct-connect assembly, in which the metal pipe and the hose are integral with each other, and then by assembling this direct-connect assembly to another component on the automotive assembly line. Also, this technique has another advantage that the number of components needed for assembly of an automobile can be reduced.
However, generally, the innermost layer of the hose, which layer is constituted by a resin layer, is poor in elasticity. Therefore, in a case where the metal pipe is connected to the hose by being press-fitted into the hose, it is difficult to ensure the sealability of the connecting portion.
Thus, it has been considered as a means for ensuring the sealability that sealing O-rings made of an elastic material are preliminarily mounted on the outer surface of the metal pipe, and that in this state, the metal pipe is connected to and press-fitted into the hose to thereby simultaneously seal between the metal pipe and the hose.
However, this sealing technique using the O-rings has encountered the problems that when the metal pipe is press-fitted into the hose, the O-rings may get out of position and that when an oscillating force is applied to the metal pipe and the hose, the O-rings may rotate in the connecting portion.
Thus, it has been considered as countermeasures that a sealing layer made of an elastic material is coated on and is bonded to the connecting portion between the metal pipe and the hose to thereby seal the connecting portion using the sealing layer.
At that time, there are two cases. In one of the cases, the sealing layer is coated on and is bonded to the outer surface of the metal pipe. In the other case, the sealing layer is coated on and is bonded to the inner surface of the hose, more specifically, the inner surface of the connecting portion at an end thereof.
However, in the case of a metal pipe used for piping of vehicles, the length of a long one of such a metal pipe is about 5 m. Therefore, it is difficult to actually form a sealing layer made of an elastic material on the outer surface of such a long metal pipe. Thus, it is advantageous to preliminarily form the sealing layer made of an elastic material on the inner surface of an end part of the hose.
The technique of forming the sealing layer made of an elastic material on the inner surface of an end part of the hose is disclosed in JP-A-9-144955.
Meanwhile, it is necessary for the hose having a resin layer as an innermost layer that the material of such a resin layer has high chemical resistance, such as low permeability of transported fluid so as to deal with various kinds of fluids.
However, such a high chemical resistance material is chemically inactive and is poor in adhesiveness. Therefore, this related technique has a problem that in a case where the sealing layer is simply formed by coating the elastic material of the sealing layer on the inner surface, the sealing layer is peeled when the metal pipe is press-fitted into the hose.